Organic light emitting display device

ABSTRACT

An organic light emitting display device includes first and second electrodes facing each other on a substrate, a charge generation layer formed between the first and second electrodes, a first light emitting stack formed between the charge generation layer and the first electrode, and a second light emitting stack formed between the charge generation layer and the second electrode, wherein a hole injection layer of a light emitting stack to realize blue color of the first and second light emitting stacks is formed by doping a host formed of hexaazatriphenylene (HAT-CN) with 0.5% to less than 10% of a dopant formed of a hole transporting material based on a volume of the hole injection layer.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. patent applicationSer. No. 14/134,149 filed on Dec. 19, 2013, which claims the benefit ofRepublic of Korea Patent Application No. 10-2012-0155899, filed on Dec.28, 2012, and Republic of Korea Patent Application No. 10-2013-0130280,filed on Oct. 30, 2013, all of which are hereby incorporated byreference in their entirety.

BACKGROUND

1. Technical Field

The present disclosure relates to an organic light emitting displaydevice with enhanced efficiency.

2. Discussion of the Related Art

In line with recent information era, the display field, which visuallydisplays electrical information signals, has rapidly developed. To meetsuch development, various flat panel display devices with excellentperformance, such as ultra-thin, lightweight, and low power consumption,have developed.

Examples of flat panel display devices include, without being limitedto, a liquid crystal display (LCD) device, a plasma display panel (PDP)device, a field emission display (FED) device, and an organic lightemitting device (OLED).

In particular, OLEDs, which are self-emissive devices, have fasterresponse time, higher luminous efficiency, higher luminance and widerviewing angles than other flat panel display devices.

A conventional organic light emitting display device includes a blueemission layer formed of a fluorescent blue material to produce whitelight. In a fluorescent blue device including the blue emission layerformed of a fluorescent blue material, however, a roll-off phenomenon inwhich luminous efficiency according to luminance decreases as luminanceincreases occurs.

SUMMARY

Accordingly, the present disclosure is directed to an organic lightemitting display device that substantially obviates one or more problemsdue to limitations and disadvantages of the related art.

An object of the present disclosure is to provide an organic lightemitting display device with enhanced efficiency.

Additional advantages, objects, and features of the disclosure will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of thedisclosure. The objectives and other advantages of the disclosure may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

To achieve these objects and other advantages and in accordance with thepurpose of the disclosure, as embodied and broadly described herein, anorganic light emitting display device includes first and secondelectrodes facing each other on a substrate, a charge generation layerformed between the first and second electrodes, a first light emittingstack formed between the charge generation layer and the firstelectrode, and a second light emitting stack formed between the chargegeneration layer and the second electrode, wherein a hole injectionlayer of a light emitting stack to realize blue color of the first andsecond light emitting stacks is formed by doping a host formed ofhexaazatriphenylene (HAT-CN) with 0.5% to less than 10% of a dopantformed of a hole transporting material based on a volume of the holeinjection layer.

The dopant may be formed of the same material as that of a holetransport layer of any one of the first and second light emittingstacks.

The first light emitting stack may include a fluorescent blue emissionlayer, and the second light emitting stack may include a phosphorescentyellow-green emission layer.

The organic light emitting display device may further include at leastone third light emitting stack formed between the second light emittingstack and the second electrode.

The dopant may be formed of the same material as that of a holetransport layer of at least one of the first, second and third lightemitting stacks.

The first and third light emitting stacks may include a fluorescent blueemission layer, and the second light emitting stack may include aphosphorescent yellow-green emission layer.

In another aspect of the present disclosure, an organic light emittingdisplay device includes first and second electrodes facing each other ona substrate, a blue emission layer formed between the first and secondelectrodes, a hole injection layer and a hole transport layer, formedbetween the blue emission layer and the first electrode, and an electrontransport layer formed between the blue emission layer and the secondelectrode, wherein the hole injection layer is formed by doping a hostformed of hexaazatriphenylene (HAT-CN) with 0.5% to less than 10% of adopant formed of a hole transporting material based on a volume of thehole injection layer.

The dopant may be formed of the same material as that of the holetransport layer.

The dopant may be formed of a material having higher hole mobility thanelectron mobility and a hole mobility of 5.0×10⁻⁵ Vs/cm² to 1.0×10⁻²Vs/cm².

A doping rate of the dopant may be 1% to 5% based on the volume of thehole injection layer.

It is to be understood that both the foregoing general description andthe following detailed description of the present disclosure areexemplary and explanatory and are intended to provide furtherexplanation as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the disclosure and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the disclosure. Inthe drawings:

FIG. 1 is a sectional view of a blue organic light emitting deviceaccording to a first embodiment of the present disclosure;

FIGS. 2A to 2C are graphs for explaining optical characteristics of anorganic light emitting display device of Comparative Example and theblue organic light emitting display device according to the firstembodiment of the present disclosure;

FIG. 3 is a sectional view of an organic light emitting display deviceaccording to a second embodiment of the present disclosure;

FIGS. 4A to 4C are graphs for explaining all-optical characteristics ofan organic light emitting display device of Comparative Example and theorganic light emitting display device according to the second embodimentof the present disclosure;

FIG. 5 is a sectional view of an organic light emitting display deviceaccording to a third embodiment of the present disclosure includingthree light emitting stacks;

FIGS. 6A and 6B are graphs for explaining all-optical characteristics ofan organic light emitting display device of Comparative Example and theorganic light emitting display device according to the third embodimentof the present disclosure; and

FIG. 7 is a sectional view of an organic light emitting display deviceaccording to the present disclosure including color filters.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments of the presentdisclosure, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

FIG. 1 is a sectional view of a blue organic light emitting deviceaccording to a first embodiment of the present disclosure.

The blue organic light emitting device of FIG. 1 includes first andsecond electrodes 102 and 104 and an organic emission layer 110 formedbetween the first and second electrodes 102 and 104.

Any one of the first and second electrodes 102 and 104 is formed as atransparent electrode or a semi-transparent electrode and the otherthereof is formed as a reflective electrode. When the first electrode102 is a semi-transparent electrode and the second electrode 104 is areflective electrode, the organic light emitting display device isembodied as a bottom emission type that emits light in a bottomdirection. When the second electrode 104 is a semi-transparent electrodeand the first electrode 102 is a reflective electrode, the organic lightemitting display device is embodied as a top emission type that emitslight in a top direction. In the present disclosure, a case in which thefirst electrode 102 as an anode is formed as a reflective electrode andthe second electrode 104 as a cathode is formed as a semi-transparentelectrode will be described by way of example.

The first electrode 102 is formed as multiple layers including a metallayer formed of aluminum (Al) or an Al alloy (e.g., AlNd) and atransparent layer formed of indium tin oxide (ITO), indium zinc oxide(IZO), or the like and serves as a reflective electrode.

The second electrode 104 is formed as a single layer or multiple layers,and each layer constituting the second electrode 104 is formed of ametal, an inorganic material, a mixture of metals, a mixture of a metaland an inorganic material, or a mixture thereof. When each layer isformed of the mixture of a metal and an inorganic material, a mix ratiothereof is 10:1 to 1:10 and, when each layer is formed of the mixture ofmetals, a mix ratio thereof is 10:1 to 1:10. The metal constituting thesecond electrode 104 may be Ag, Mg, Yb, Li, or Ca, the inorganicmaterial constituting the second electrode 104 may be Li₂O, CaO, LiF, orMgF₂, and the metal and the inorganic material facilitate migration ofelectrons and thus enable a large amount of electrons to be supplied tothe organic emission layer 110.

A hole injection layer (HIL) 112, a hole transport layer (HTL) 114, anemission layer (EML(B)) 116, and an electron transport layer (ETL) 118are sequentially formed between the first and second electrodes 102 and104.

The HIL 112 facilitates injection of holes from the first electrode 102.The HTL 114 supplies the holes from the HIL 112 to the EML(B) 116. TheETL 118 supplies electrons from the second electrode 104 to the EML(B)116.

The holes supplied via the HTL 114 and the electrons supplied via theETL 118 are recombined in the EML(B) 116, whereby light is emitted. Inparticular, the EML(B) 116 is formed of a fluorescent blue material andthus realizes blue color.

The HIL 112 of the organic light emitting display device according tothe first embodiment of the present disclosure is formed by doping ahost 112 a with 0.5% to less than 10% of a dopant 112 b based on avolume of the HIL 112 and has a thickness of about 7 nm or less. In thisregard, the dopant 112 b may be doped on the host 112 a with a dopingrate of 1 to 5% based on the volume of the HIL 112. The host 112 a isformed of hexaazatriphenylene (HAT-CN), and the dopant 112 b is formedof a hole transporting material having higher hole mobility thanelectron mobility. In this regard, the hole transporting material may bea material having a hole mobility of 5.0×10⁻⁵ Vs/cm² to 1.0×10⁻² Vs/cm².For example, the hole transporting material may be at least one ofN,N-dinaphthyl-N,N′-diphenyl benzidine (NPD),N,N′-bis-(3-methylphenyl)-N,N′-bis-(phenyl)-benzidine (TPD), s-TAD, and4,4′,4″-Tris(N-3-methylphenyl-N-phenylamino)-triphenylamine (MTDATA),and a material for forming the HTL 114 may be used as the holetransporting material. Accordingly, the hole mobility of the HIL 112 isenhanced and thus hole injection characteristics at an interface betweenthe HIL 112 and the HTL 114 are enhanced. As a result, a formation rateof excitons formed through combination between electrons and holesincreases due to stable charge balance in the EML(B) 116 and,accordingly, luminous efficiency is enhanced.

FIGS. 2A to 2C are graphs for explaining optical characteristics oforganic light emitting display devices of Comparative Example andExample 1.

In particular, as illustrated in FIG. 2A, the organic light emittingdisplay device of Example 1 including the HIL 112 doped with 1 to 3% ofthe dopant 112 b has higher peak intensity than that of the organiclight emitting display device of Comparative Example including an HILthat is undoped with a dopant and thus, as shown in Table 1 below, theorganic light emitting display device of Example 1 has higher efficiencyat 10 mA/cm², increased by 7% or greater, than that of the organic lightemitting display device of Comparative Example.

TABLE 1 10 mA/cm² Color Color Efficiency coordinate coordinate (Cd/A) QE(%) (CIEx) (CIEy) Roll off Comparative 8.0 9.6 0.136 0.092 0.93 ExampleExample 1 8.6 10.3 0.137 0.092 1.05

In addition, as illustrated in FIG. 2B, a blue light emitting deviceincluding the HIL 112 doped with 1 to 3% of the dopant 112 b hasincreased luminous efficiency in the entire luminance region whencompared to blue light emitting devices of Comparative Examplesrespectively including an undoped HIL, an HIL doped with 10% of adopant, and an HIL doped with 20% of a dopant. In addition, as shown inTable 1, the organic light emitting display device of Example 1 has aroll-off factor (a ratio of efficiency at a current density of 50 mA/cm²to efficiency at a current density of 10 mA/cm²) of 1.05, which ishigher than that of the organic light emitting display device ofComparative Example having a roll-off factor of 0.93. From the results,it can be confirmed that the blue organic light emitting deviceaccording to the first embodiment of the present disclosure undergoesreduced roll-off phenomenon in which efficiency is decreased in a highluminance region.

In particular, it can be confirmed that the blue light emitting deviceincluding the HIL 112 doped with 1 to 3% of the dopant 112 b undergoesless roll-off phenomenon in which efficiency is decreased in a highluminance region than the blue light emitting devices respectivelyincluding the HIL doped with 10% of a dopant and the HIL doped with 20%of a dopant. Thus, in the blue light emitting device according to thefirst embodiment of the present disclosure, a doping rate of the dopant112 b of the HIL 112 may be 0.5% to less than 10% based on the volume ofthe HIL 112.

In addition, as illustrated in FIG. 2C, it can be confirmed that, eventhough different types of materials (e.g., NPD, TPD, s-TAD, and MTDATA)for forming the dopant 112 b are used, the blue light emitting device ofExample including the HIL 112 doped with 1 to 3% of the dopant 112 b hasenhanced luminous efficiency in the entire luminance region whencompared to the blue light emitting device of Comparative Example.Although NPD, TPD, s-TAD, and MTDATA have been described as dopantmaterials by way of example, various other hole transporting materialsmay be used as dopant materials and the same effect may be obtainedusing the dopant materials.

FIG. 3 is a sectional view of an organic light emitting display deviceaccording to a second embodiment of the present disclosure.

The organic light emitting display device of FIG. 3 includes the sameelements as those of the organic light emitting display device of FIG.1, except that the organic light emitting display device of FIG. 3 has atwo-stack structure. Thus, a detailed description of the same elementswill be omitted herein.

The organic light emitting display device of FIG. 3 includes the firstand second electrodes 102 and 104 facing each other, first and secondlight emitting stacks 110 and 120 formed between the first and secondelectrodes 102 and 104, and a charge generation layer (CGL) 130 disposedbetween the first and second light emitting stacks 110 and 120. In thepresent embodiment, two light emitting stacks are used, but embodimentsare not limited thereto. That is, at least three light emitting stacksmay be formed.

The first light emitting stack 110 is formed between the first electrode102 and the charge generation layer 130. The first light emitting stack110 includes the HIL 112, a first HTL 114, a first EML(B) 116, and afirst ETL 118 that are sequentially formed on the first electrode 102.

The second light emitting stack 120 is formed between the secondelectrode 104 and the charge generation layer 130. The second lightemitting stack 120 includes a second HTL 124, a second EML(YG) 126, anda second ETL 128 that are sequentially formed on the charge generationlayer 130.

The first EML(B) 116 includes a fluorescent blue dopant and host to emitblue light, and the second EML(YG) 126 includes a phosphorescentyellow-green dopant and host to emit orange light. Accordingly, the bluelight of the first EML(B) 116 and the orange light of the second EML(YG)126 may be realized as white light through mixing. In addition, whitelight may be emitted using other fluorescent dopants and phosphorescentdopants.

The charge generation layer 130 is formed between the first and secondlight emitting stacks 110 and 120 and controls charge balance betweenthe first and second light emitting stacks 110 and 120. The chargegeneration layer 130 includes an N-type charge generation layer 132 anda P-type charge generation layer 134 that are sequentially stacked.

The N-type charge generation layer 132 injects electrons into the firstlight emitting stack 110, and the P-type charge generation layer 134injects holes into the second light emitting stack 120.

The electrons transferred to the first light emitting stack 110 via theN-type charge generation layer 132 and holes transferred via the HIL 112and the first HTL 114 are combined in the first EML(B) 116 of the firstlight emitting stack 110, forming excitons and releasing energy, wherebyvisible light is emitted.

The holes transferred to the second light emitting stack 120 via theP-type charge generation layer 134 and electrons transferred via thesecond electrode 104 and the second ETL 128 are combined in the secondEML(YG) 126 of the second light emitting stack 120, forming excitons andreleasing energy, whereby visible light is emitted.

In the organic light emitting display device according to the secondembodiment of the present disclosure, the HIL 112 of the first lightemitting stack 110 to emit blue light is formed by doping the host 112 awith 0.5% to less than 10% of the dopant 112 b based on a volume of theHIL 112 and has a thickness of about 7 nm or less. In this regard, thedopant 112 b may be doped on the host 112 a with a doping rate of 1 to5% based on the volume of the HIL 112. The host 112 a is formed ofhexaazatriphenylene (HAT-CN), and the dopant 112 b is formed of a holetransporting material having higher hole mobility than electronmobility. In this regard, the hole transporting material may be amaterial having a hole mobility of 5.0×10⁻⁵ Vs/cm² to 1.0×10⁻² Vs/cm².For example, the hole transporting material may be at least one of NPD,TPD, s-TAD, and MTDATA, and materials for forming the first and secondHTLs 114 and 124 of the first and second light emitting stacks 110 and120 may be used as the hole transporting material. Accordingly, the holemobility of the HIL 112 of the first light emitting stack 110 isenhanced and thus hole injection characteristics at an interface betweenthe HIL 112 and the first HTL 114 of the first light emitting stack 110are enhanced. As a result, a formation rate of excitons formed throughcombination between electrons and holes increases due to charge balancein the first EML(B) 116 and, accordingly, luminous efficiency isenhanced.

FIGS. 4A to 4C are graphs for explaining all-optical characteristics oforganic light emitting display devices of Comparative Example andExample 2.

In particular, as illustrated in FIG. 4A, the organic light emittingdisplay device of Example 2 including the HIL 112 of the first lightemitting stack 110, doped with 1 to 3% of the dopant 112 b, has higherpeak intensity (blue peak) of the first EML(B) 116 to realize blue colorand higher peak intensity (YG peak) of the second EML(YG) 126 to realizeorange color than those of the organic light emitting display device ofComparative Example including an HIL of a first light emitting stack,undoped with a dopant and thus, as shown in Table 2 below, the organiclight emitting display device of Example 2 has higher efficiency at 10mA/cm², increased by 6% or greater, than that of the organic lightemitting display device of Comparative Example.

TABLE 2 10 mA/cm² Color Color Efficiency coordinate coordinate (Cd/A) QE(%) (CIEx) (CIEy) Roll off Comparative 81.1 32.0 0.317 0.339 0.81Example Example 2 86.5 35.1 0.324 0.330 0.84

In addition, as illustrated in FIG. 4B, the organic light emittingdisplay device of Example 2 including the HIL 112 of the first lightemitting stack 110, doped with 1% to 3% of the dopant 112 b, has higherluminous efficiency in the entire luminance region than that of organiclight emitting display devices of Comparative Examples respectivelyincluding an HIL of a first light emitting stack, undoped with a dopant,an HIL of a first light emitting stack, doped with 10% of a dopant, andan HIL of a first light emitting stack, doped with 20% of a dopant. Inaddition, as shown in Table 2, the organic light emitting display deviceof Example 2 has a roll-off factor (a ratio of efficiency at a currentdensity of 50 mA/cm² to efficiency at a current density of 10 mA/cm²) of0.84, which is higher than that of the organic light emitting displaydevice of Comparative Example having a roll-off factor of 0.81. From theresults, it can be confirmed that the organic light emitting displaydevice having a multi-stack light emitting structure according to thesecond embodiment of the present disclosure undergoes reduced roll-offphenomenon in which efficiency is decreased in a high luminance region.

In particular, it can be confirmed that the organic light emittingdisplay device of Example 2 including the HIL 112 of the first lightemitting stack 110, doped with 1% to 3% of the dopant 112 b, undergoesless roll-off phenomenon in which efficiency is decreased in a highluminance region than the organic light emitting devices respectivelyincluding the HIL doped with 10% of a dopant and the HIL doped with 20%of a dopant. Thus, in the organic light emitting display deviceaccording to the second embodiment of the present disclosure, a dopingrate of the dopant 112 b of the HIL 112 of the first light emittingstack 110 may be 0.5% to less than 10%.

In addition, as illustrated in FIG. 4C, it can be confirmed that, eventhough different types of materials (e.g., NPD and TPD) for forming thedopant 112 b are used, the organic light emitting display device ofExample 2 including the HIL 112 doped with 1% to 3% of the dopant 112 bhas enhanced luminous efficiency in the entire luminance region whencompared to the organic light emitting display device of ComparativeExample. Although NPD and TPD have been described as dopant materials byway of example, various other hole transporting materials may be used asdopant materials and the same effect may be obtained using the dopantmaterials.

In the second embodiment of the present disclosure, two light emittingstacks are used, but embodiments are not limited thereto. That is, atleast three light emitting stacks may be formed. For example, asillustrated in FIG. 5, three light emitting stacks, e.g., first, secondand third light emitting stacks 110, 120 and 140, may be formed.

An organic light emitting display device illustrated in FIG. 5 includesthe first and second electrodes 102 and 104 facing each other, thefirst, second and third light emitting stacks 110, 120 and 140 formedbetween the first and second electrodes 102 and 104, and chargegeneration layers 130 respectively disposed between the first and secondlight emitting stacks 110 and 120 and between the second and third lightemitting stacks 120 and 140.

The first light emitting stack 110 is formed between the first electrode102 and the charge generation layer 130. The first light emitting stack110 includes the HIL 112, the first HTL 114, the first EML(B) 116, andthe first ETL 118 that are sequentially formed on the first electrode102.

The second light emitting stack 120 is formed between the first andthird light emitting stacks 110 and 140. The second light emitting stack120 includes the second HTL 124, the second EML(YG) 126, and the secondETL 128 that are sequentially formed on the charge generation layer 130.

The third light emitting stack 120 is formed between the secondelectrode 104 and the charge generation layer 130. The third lightemitting stack 120 includes a third HTL 144, a third EML(B) 146, and athird ETL 148 that are sequentially formed on the charge generationlayer 130.

The first and third EMLs(B) 116 and 146 include a fluorescent bluedopant and host to emit blue light, and the second EML(YG) 126 includesa phosphorescent yellow-green dopant and host to emit orange light.Accordingly, the blue light of the first and third EMLs(B) 116 and 146and the orange light of the second EML(YG) 126 may be realized as whitelight through mixing. In particular, a structure of the organic lightemitting display device according to a third embodiment of the presentdisclosure differs from that of the organic light emitting displaydevice of FIG. 3 in that the organic light emitting display deviceaccording to the third embodiment further includes the third EML(B) 146to realize blue color. In addition, white light may be realized usingother fluorescent dopants and phosphorescent dopants.

The charge generation layers 130 are respectively formed between thefirst and second light emitting stacks 110 and 120 and between thesecond and third light emitting stacks 120 and 140 and control chargebalance among the first, second and third light emitting stacks 110, 120and 140. Each charge generation layer 130 includes an N-type chargegeneration layer 132 and a P-type charge generation layer 134 that aresequentially stacked.

The N-type charge generation layer 132 injects electrons into the firstand second light emitting stacks 110 and 120, and the P-type chargegeneration layer 134 injects holes into the second and third lightemitting stacks 120 and 140.

The electrons transferred to the first light emitting stack 110 via theN-type charge generation layer 132 and holes transferred via the HIL 112and the first HTL 114 are combined in the first EML(B) 116 of the firstlight emitting stack 110, forming excitons and releasing energy, wherebyvisible light is emitted.

The electrons transferred to the second light emitting stack 120 via theN-type charge generation layer 132 and holes transferred to the secondlight emitting stack 120 via the P-type charge generation layer 134 arecombined in the second EML(YG) 126 of the second light emitting stack120, forming excitons and releasing energy, whereby visible light isemitted.

The holes transferred to the third light emitting stack 140 via theP-type charge generation layer 134 and electrons transferred via thesecond electrode 104 and the third ETL 148 are combined in the thirdEML(B) 146 of the third light emitting stack 140, forming excitons andreleasing energy, whereby visible light is emitted.

In the organic light emitting display device according to the thirdembodiment of the present disclosure, the HIL 112 of the first lightemitting stack 110 to emit blue light is formed by doping the host 112 awith the dopant 112 b with a doping rate of 0.5% to less than 10% basedon a volume of the HIL 112 and has a thickness of about 7 nm or less. Inthis regard, the dopant 112 b may be doped on the host 112 a in a dopingrate of 1% to 5% based on the volume of the HIL 112. The host 112 a isformed of HAT-CN, and the dopant 112 b is formed of a hole transportingmaterial having higher hole mobility than electron mobility. In thisregard, the hole transporting material may be a material having a holemobility of 5.0×10⁻⁵ Vs/cm² to 1.0×10⁻² Vs/cm². For example, the holetransporting material may be at least one of NPD, TPD, s-TAD, andMTDATA, and a material for forming at least one of the first, second andthird HTLs 114, 124 and 144 of the first, second and third lightemitting stacks 110, 120 and 140 may be used as the hole transportingmaterial. Accordingly, the hole mobility of the HIL 112 of the firstlight emitting stack 110, including a hole transporting material, isenhanced and thus hole injection characteristics at an interface betweenthe HIL 112 and the first HTL 114 of the first light emitting stack 110are enhanced. As a result, a formation rate of excitons formed throughcombination between electrons and holes increases due to charge balancein the first EML(B) 116 and, accordingly, luminous efficiency isenhanced.

FIGS. 6A and 6B are graphs for explaining all-optical characteristics oforganic light emitting display devices of Comparative Example andExample 3.

In particular, as illustrated in FIG. 6A, the organic light emittingdisplay device of Example 3 including the HIL 112 of the first lightemitting stack 110, doped with the dopant 112 b, has higher peakintensity (blue peak) of the first EML(B) 116 to realize blue color andhigher peak intensity (YG peak) of the second EML(YG) 126 to realizeorange color than those of the organic light emitting display device ofComparative Example including an HIL of a first light emitting stack,undoped with a dopant and thus, as shown in Table 3 below, the organiclight emitting display device of Example 3 has higher efficiency at 10mA/cm², increased by 2.9% or greater, than that of the organic lightemitting display device of Comparative Example.

TABLE 3 10 mA/cm² Efficiency (Cd/A) Roll off Comparative Example 84.90.85 Example 3 87.8 0.87

In addition, as illustrated in FIG. 6B, the organic light emittingdisplay device of Example 3 including the HIL 112 of the first lightemitting stack 110, doped with 1 to 3% of the dopant 112 b, has higherluminous efficiency in the entire luminance region than that of theorganic light emitting display device of Comparative Example includingan HIL of a first light emitting stack, undoped with a dopant. Inaddition, the organic light emitting display device of Example 3 has aroll-off factor (a ratio of efficiency at a current density of 50 mA/cm²to efficiency at a current density of 10 mA/cm²) of 0.87, which ishigher than that of the organic light emitting display device ofComparative Example having a roll-off factor of 0.85. From the results,it can be confirmed that the organic light emitting display devicehaving a multi-stack light emitting structure according to the thirdembodiment of the present disclosure undergoes reduced roll-offphenomenon in which efficiency is decreased in a high luminance region.

The organic light emitting display devices according to the presentdisclosure may be applied to a structure having red, green and bluecolor filters 150R, 150G and 150B as illustrated in FIG. 7. White lightgenerated via the first and second light emitting stacks 110 and 120illustrated in FIG. 3 or white light generated via the first, second andthird light emitting stacks 110, 120 and 140 illustrated in FIG. 5 isemitted as red light while passing through a sub-pixel region providedwith the red color filter 150R, is emitted as green light while passingthrough a sub-pixel region provided with the green color filter 150G, isemitted as blue light while passing through a sub-pixel region providedwith the blue color filter 150B, and is emitted unchanged while passingthrough a sub-pixel region not provided with a color filter.

As is apparent from the foregoing description, in organic light emittingdisplay devices according to the present disclosure, a hole injectionlayer is formed by doping a host formed of HAT-CN with a holetransporting material. Accordingly, hole mobility of the hole injectionlayer is enhanced and thus hole injection characteristics at aninterface between the hole injection layer and a hole transport layerare enhanced. As a result, a formation rate of excitons formed throughcombination between electrons and holes increases due to stable chargebalance in an emission layer and thus luminous efficiency may beenhanced and a roll-off phenomenon may also be reduced. In particular,when the organic light emitting display devices according to the presentdisclosure are applied to a large area display panel, power consumptionmay be reduced.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present disclosurewithout departing from the spirit or scope of the disclosure. Thus, itis intended that the present disclosure covers the modifications andvariations of this disclosure provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. An organic light emitting display devicecomprising: a first electrode and a second electrode facing each otheron a substrate; a charge generation layer formed between the firstelectrode and the second electrode; a first light emitting stack formedbetween the charge generation layer and the first electrode; and asecond light emitting stack formed between the charge generation layerand the second electrode, wherein one of the first and second lightemitting stacks emits a blue light, and wherein a hole injection layerof one of the first and second light emitting stacks emitting blue lightis formed by doping a host formed of hexaazatriphenylene (HAT-CN) with0.5 vol. % to less than 10 vol. % of a dopant that is a holetransporting material based on a volume of the hole injection layer. 2.The organic light emitting display device according to claim 1, whereinthe dopant is the same material as that of a hole transport layer of anyone of the first light emitting stack and the second light emittingstack.
 3. The organic light emitting display device according to claim1, wherein the dopant is a material having a hole mobility higher thanan electron mobility, the hole mobility from 5.0×10⁻⁵ Vs/cm² to 1.0×10⁻²Vs/cm².
 4. The organic light emitting display device according to claim1, wherein a doping rate of the dopant is 1 vol. % to 5 vol. % based onthe volume of the hole injection layer.
 5. The organic light emittingdisplay device according to claim 1, wherein the first light emittingstack comprises a fluorescent blue emission layer, and the second lightemitting stack comprises a phosphorescent yellow-green emission layer.6. The organic light emitting display device according to claim 1,further comprising at least one third light emitting stack formedbetween the second light emitting stack and the second electrode.
 7. Theorganic light emitting display device according to claim 6, wherein thedopant is a same material as that of a hole transport layer of at leastone of the first light emitting stack, the second light emitting stack,and the third light emitting stack.
 8. The organic light emittingdisplay device according to claim 6, wherein the dopant is a materialhaving a hole mobility higher than an electron mobility, the holemobility from 5.0×10⁻⁵ Vs/cm² to 1.0×10⁻² Vs/cm².
 9. The organic lightemitting display device according to claim 6, wherein a doping rate ofthe dopant is 1 vol. % to 5 vol. % based on the volume of the holeinjection layer.
 10. The organic light emitting display device accordingto claim 6, wherein the first light emitting stack and the third lightemitting stack comprise a fluorescent blue emission layer, and thesecond light emitting stack comprises a phosphorescent yellow-greenemission layer.
 11. An organic light emitting display device comprising:a first electrode and a second electrode facing each other on asubstrate; a first light emitting stack comprising: a blue emissionlayer between the first electrode and the second electrode; a holeinjection layer and a hole transport layer, between the blue emissionlayer and the first electrode; and an electron transport layer betweenthe blue emission layer and the second electrode; a second lightemitting stack including a phosphorescent yellow-green emission layerbetween the first light emitting stack and the second electrode; and acharge generation layer between the first and second light emittingstacks; a third light emitting stack including a fluorescent blueemission layer between the second light emitting stack and the secondelectrode; and a second charge generation layer between the second andthird light emitting stacks, wherein the hole injection layer iscomposed by doping a host composed of hexaazatriphenylene (HAT-CN) with1 vol. % to less than 3 vol. % of a dopant that is a hole transportingmaterial based on a volume of the hole injection layer, wherein thedopant is composed of at least one of N,N-dinaphthyl-N,N′-diphenylbenzidine (NPD), N,N′-bis-(3-methylphenyl)-N,N′-bis-(phenyl)-benzidine(TPD), and s-TAD.